Horner & T. rex

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>>                        I was fortunate enough to go to the dedication of
>>the T-rex in UC Berkeley today. The guest lecturer was John Horner. 

Just hoping I get invited as a guest speaker at a hadro function sometime :-(

>and discuss several dino issues.  Just for fun I showed each of them a
theropod
>tooth I found in Montana this summer and asked them to identify it.  A
Berkeley
>grad student (supposedly a tooth expert) said definitely Albertosaurid,
>possibly Daspletasaur.  Another Horner grad student had said the same.
>Padian declined to venture a guess.  Horner was positive it was a Dromaesaurid
>tooth.h!

Just a note: Horner is a hadrosaur specialist.  Having some pretty good
ideas as to who the Berkeley and U Montana grads are, I'd go with their
conclusions.

>I took notes during Horner's "T.rex as scavenger" talk; his points are
>summarized below.  I am still unconvinced, but I now have a much better
>appreciation for that viewpoint.  His arguments are:
>
>       - Predators *need* arms to catch prey.
>         T.rex arms are too small, with too limited movement to be used
>         to catch prey.

Tell that to wolves, Lycaon pictus, and phorusrachids!

>     - Fast runners have long shin bones compared to thigh bones.
>         T.rex has shin, thigh bones of equal length, so it must have
>         been a walker (conflicts somewhat with his book, where he allows
>         for the possibility of a 25 mph T.rex.)  

Smaller tyrannosaurids have shins which are longer than their thighs.  No
other >4 tonne animal has as long a shin relative to thigh as Tyrannosaurus.

>     - Predators need good vision, therefore large eyes.
>         T.rex had comparatively small eyes, and small optic lobe.

It has not been demonstrated that tyrannosaurid eyes are too small.
Relative eye size decreases faster than overall body size: compare the eyes
of foxes to wolves, small cats to tigers, Hyracotherium to Equus, etc.

>     - T.rex had unusually large olfactory lobe; implies especially
>         acute sense of smell.  Only 2 other animals in history ever had a 
>         proportionally larger olfactory lobe:  kiwi and turkey vulture,
>         one of which is a scavenger.

And one of which is an omnivore, so what does it all mean?  Furthermore,
when was the last survey of the relative size of the olfactory lobes in
dinosaurs: the 1920s?

>     - T.rex teeth are often found among mono-specific bone bed sites;
>         implies T.rex was scavenging the mass deaths in herbivore herds.

So what?  Dromaeosaurid teeth are also found there.  Almost no predator
(except for some snakes, perhaps) will pass up a chance to scavenge.
>
>These are good arguments, but I believe there are good rebuttals to each.
>Certainly T.rex scavenged opportunistically, but I still don't buy Horner's
>scavenger-only idea.  I did challenge Jack on a couple of points:
>
>1. I asked why T.rex would need stereo vision if it only scavenged.
>   He said stereo vision is a primitive feature that T.rex just inherited,
>   although it has no need for it.

Ummm, no.  Albertosaurus, Daspletosaurus, and other basal tyrannosaurids do
not show the well developed potential for stereoscopic vision.

>
>2. I asked how he would explain the recent find where T.rex tooth mark
>   was found in a herbivore bone that had healed over, implying the
>   dinosaur had escaped and survived a T.rex attack.  His answer was,
>   "it's not a T.rex tooth mark".

Isn't this a Lancian bone?  If so, what other predator could there have been
of that size in the U.S. during the latest Maastrichtian?
>
>Still, he made a reasonable case even though he is not as serious about it
>as he seems.  In "The Complete T.rex" Horner admits that he is not sure
>about the scavenger theory, but he often talks that way when talking to
>others, just to take up a contrary position.

Fair enough.



Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084